The invention pertains to compression fittings utilizing compression nuts and axial displaceable ferrules or bushings.
The usual compression fitting construction includes an annular recess into which the tube to be connected is bottomed, a ferrule or bushing receiving surface is defined adjacent the tube recess, and a compression nut encircling the tube axially compresses the ferrule into the fitting recess to cause a radial compression of the ferrule which establishes a completed sealed mechanical connection between the tube and fitting.
Compression fittings are widely used in the plumbing arts, and in the use of this type of fitting it is standard practice to investigate to insure that the tube is "bottomed" in the fitting recess during rotation of the compression nut. The dimensional relationships of most compression fittings are so designed that proper sealing and operation occurs when the tube bottoms against the tube receiving recess defined therein, and it is important that the tube end be maintained against the recess receiving shoulder in order to prevent the end of the tube from collapsing due to the radial forces imposed thereon by the ferrule or bushing, and this relationship is further important to assure proper interrelationship between the ferrule, the tube and the ferrule engaging fitting surfaces.
It is not uncommon, particularly where access and visibility of the compression fitting is hindered, for the operator to attempt to interconnect a compression fitting and tube when the tube has become partially withdrawn from the fitting recess as the operator will not be aware of such condition. Accordingly, difficulty in producing an effective compression fitting seal is often experienced when the connection has been made under adverse conditions.
Another problem often encountered in the utilization of compression fittings results from rotation of the tube relative to the fitting as the compression nut is rotated to force the ferrule into a sealed relationship with the tube. Ideally, during assembly of a compression fitting, only the compression nut rotates relative to the fitting body, and the tube and ferrule are nonrotative. However, because of frictional factors, burrs, foreign matter, or for other reasons, it is not uncommon for the ferrule or bushing to rotate with the compression nut, imparting a rotative torque on the tube. This tendency for the tube to rotate, with the ferrule, will often result in an improper seal between the ferrule and the tube resulting in a leaking joint. While the operator may grasp the tube to retain the same against rotation such manual operation becomes difficult in many instances because of clearance problems, and the applying of a wrench or pliers to the tube to retain the same against rotation may easily result in tube damage.